Summary of work: Cell cycle progression is subject to numerous checkpoints, which serve to arrest growth if certain processes are incomplete, or damage is incurred. While treatment of cells with toxic agents often leads to activation of one or more of these checkpoints and results in growth arrest, in some instances such treatment leads to apoptosis. The factors responsible for determining whether a cell will undergo apoptosis or growth arrest have yet to be clarified and this is the focus of this project. Several model systems are being employed to address these questions. In one study we are investigating the mechanism whereby TGFbeta can prevent serum deprivation-induced apoptosis in human lung carcinoma A549 cells. Protection by TGFbeta is associated with the early induction of c-Jun expression, but a later suppression of c-Jun-N-terminal kinase (JNK) activity. Induction of c- Jun appears to be mediated via Smad3/Smad4. Expression of dominant negative mutant forms of either c-Jun or Smad3/Smad4 proteins partially inhibits the protective influence of TGFbeta while expression of a dominant negative form of the kinase SEK1, which is necessary for JNK activation, mimics the effect of TGFbeta. These findings suggest that early Smad-dependent expression of c-Jun is important for survival, as is inhibition of JNK at later time points. A second study is examining the role of c-Jun-N-terminal kinase 2 (JNK2) in regulating tumor cell growth using an antisense strategy to selectively prevent JNK1 and JNK2 expression and activites. We have observed that inhibition of JNK2 expression leads to marked growth inhibition and apoptosis of certain cancer cell lines. This effect appears to be restricted to cells lacking p53 function and correlates with an inability of p53-deficient cells to express the p53 effector protein p21/Waf1/Cip1. Current studies are addressing the mechanisms contributing to this effect using a SAGE approach to identify genes differentially expressed in control and JNK2 antisense-treated cells. - genotoxic stress, apoptosis, TGFbeta, p53, mitogen-activated protein kinase, JNK, antisense